It has been tested on an actual DS, so I'm sure it's not the emulator's fault.

All I have done was edit the image:

It works fine.
but when I pause the game and go back...

It's an LZ77 compressed image but I've recompressed it back after editing.
There was no weird process; it was just a extract -> decompress -> edit -> recompress -> insert
It happens on ALL of the images.

but when I do something else and go back to the screen, it's normal again.

another example:

http://mfiles.naver.net/66b453889dccab1d33...%BF%F8%BA%BB.lz
this is the original file.
The file is set up in this way:
0000 ~ 0004 = Magic stamp
0004 ~ 0008 = Palette pointer
0008 ~ 000C = ??
000C ~ 003C = Pointer information. Needs editing after image is edited.
003C ~ 023C = Palette. This is the palette of all 6 sub images.
and then comes the 6 strips of LZ77 compressed images.

As you can see in the 3rd screen, both top screen and the bottom screen uses the same picture. So I don't think it's the edit that went wrong, because if I used the wrong palette, all of the same color would be shown as black.

@Hehe Moo
don't know what you are talking about.
It's gonna be a full translation. All of the texts have been tested and works. It's just the graphics that I have problems on. And as you can see in the screens, yes only the bottom screen is weird.

I think there is ANOTHER palette somewhere in the ROM that the bottom screen uses, but I'm not sure. Probably it is caused because of the increased file size. Maybe not. But usually, the palette would be with the picture.
So I THINK another palette is somewhere in the ROM, and I have to switch pointers to redirect to the new offset... I'm not sure.

Psycoblaster, It seems one colour of your image has changed to the transparent color (you know, in each palette in an image, there is one). What program do you use to edit the image? I edited PW3 for a translation to spanish with Tile Molester and there was a duplicated color in the palette, obvious was the transparent one. If this in't the case, try to change the "black" area with a similar color present into the image, it's easy indexing image to edit with photoshop.

well what I don't get is that it's fine. It looks normal. But when I pause the game and go back, the white gets screwed up. I'll look into it to see if it is the transparent color. But I haven't touched ANYTHING in the white areas. Probably because I edited with photoshop, and when it saved, it used the transparent white color?
I've already tried using a different color. It works, because it's not white.
If it doesn't work at all, I might just use a color very similar to white and use it instead of the white.